1. Field of the Invention
The present invention relates to an ink-jet printhead, and a method for manufacturing the same, in which an ink passage is formed parallel to a surface of a substrate on a same plane as an ink chamber using an etch method to improve performance of the printhead.
2. Description of the Related Art
In general, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of a printing ink at a desired position on a recording sheet. Ink ejection mechanisms of an ink-jet printhead are largely categorized into two different types: an electro-thermal transducer type (bubble-jet type), in which a heat source is employed to form and expand a bubble in ink thereby causing an ink droplet to be ejected, and an electromechanical transducer type, in which an ink droplet is ejected by a change in volume in ink due to a deformation of a piezoelectric element.
An ink droplet ejection mechanism of a thermal ink-jet printhead will now be described in detail. When a pulse current flows through a heater formed of a resistive heating material, heat is generated by the heater. The heat causes ink near the heater to be rapidly heated to approximately 300° C., thereby boiling the ink and generating a bubble in the ink. The formed bubble expands and exerts pressure on ink contained within an ink chamber. This pressure causes a droplet of ink to be ejected through a nozzle from the ink chamber.
A thermal driving method includes a top-shooting method, a side-shooting method, and a back-shooting method depending on the direction in which the ink droplet is ejected and the direction in which a bubbles expands. The top-shooting method is a method in which the growth direction of a bubble is the same direction as the ejection direction of an ink droplet. The side-shooting method is a method in which the growth direction of a bubble is perpendicular to the ejection direction of an ink droplet. The back-shooting method is a method in which the growth direction of a bubble is opposite to the ejection direction of an ink droplet.
An ink-jet printhead using the thermal driving method should satisfy the following requirements. First, manufacturing of the ink-jet printhead has to be simple, costs have to be low, and mass production thereof has to be possible. Second, in order to obtain a high-quality image, crosstalk between adjacent nozzles has to be suppressed and an interval between adjacent nozzles has to be narrow, that is, a plurality of nozzles should be densely arranged to improve dots per inch (DPI). Third, in order to perform a high-speed printing operation, a period in which the ink chamber is refilled with ink after ejection of an ink droplet from the ink chamber has to be as short as possible. That is, heated ink has to be quickly cooled to increase a driving frequency.
FIG. 1 illustrates a perspective view of a structure of a conventional ink-jet printhead using a back-shooting method. Referring to FIG. 1, an ink-jet printhead 24 includes a substrate 11 on which a nozzle 10 through which ink droplets are ejected, and an ink chamber 16 to be supplied with ink to be ejected are formed, a cover plate 3 in which a through hole 2 for providing communication between the ink chamber 16 and an ink reservoir 12 is formed, and the ink reservoir 12 for supplying ink to the ink chamber 16. The substrate 11, the cover plate 3, and the ink reservoir 12 are sequentially stacked. In addition, a heater 42 is arranged in a ring shape around the nozzle 10 of the substrate 11.
In the above structure, when pulse current is supplied to the heater 42 and heat is generated by the heater 42, ink in the ink chamber 16 is boiled, and bubbles are generated and continuously expand. Due to this expansion, pressure is applied to ink filling the ink chamber 16 such that ink droplets are ejected through the nozzle 10. Subsequently, ink flows into the ink chamber 16 through the through hole 2 formed in the cover plate 3 from the ink reservoir 12. Thus, the ink chamber 16 is refilled with ink.
In this ink-jet printhead, however, a depth of the ink chamber 16 is almost the same as a thickness of a substrate 11. Thus, unless a very thin substrate is used, the size of the ink chamber increases. Accordingly, pressure generated in bubbles to be used to eject ink is dispersed by ambient ink, which lowers an ejection property. When a thin substrate is used to reduce the size of the ink chamber, it becomes more difficult to process the substrate. That is, a depth of an ink chamber, which is generally used in an ink-jet printhead, is about 10-30 μm. In order to form an ink chamber having that depth, a silicon substrate having a thickness of 10-30 μm should be used. It is virtually impossible, however, to process a silicon substrate having such a thickness in a semiconductor manufacturing process.
Further, in order to manufacture an ink-jet printhead having the above structure, a cover plate and an ink reservoir are bonded together. Thus, a process of manufacturing such an ink-jet printhead becomes complicated, and an ink passage, which affects an ejection property, cannot be elaborately formed.
FIG. 2 illustrates a cross-sectional view of a structure of a conventional ink-jet printhead using a back-shooting method. Referring to FIG. 2, an ink chamber 15 having a hemispherical shape is formed on a substrate 30 formed of silicon. A manifold 26 for supplying ink to an ink chamber 15 is formed below the ink chamber 15. An ink channel 13 for providing communication between the ink chamber 15 and the manifold 26 is formed between the ink chamber 15 and the manifold 26 in a cylindrical shape perpendicular to a surface of the substrate 30. A nozzle plate 20, in which a nozzle 21 through which ink droplets 18 are ejected is formed, is placed on the surface of the substrate 30 and forms an upper wall of the ink chamber 15. A ring-shaped heater 22 is formed in the nozzle plate 20, adjacent to the nozzle 21, and surrounds the nozzle 21. An electric line (not shown) for applying current is connected to the heater 22.
In the above structure, ink supplied through the manifold 26 and the ink channel 13 fills the ink chamber 15. In this state, when pulse current is applied to the ring-shaped heater 22, ink below the heater 22 is boiled by heat generated by the heater 22, and bubbles are generated. As a result, pressure is applied to ink within the ink chamber 15, and ink in the vicinity of the nozzle 21 is ejected in the shape of an ink droplet 18 through the nozzle 21. Subsequently, ink flows into the ink chamber 15 through the ink channel 13, thereby refilling the ink chamber 15 with ink.
In such an ink-jet printhead, only part of a substrate is etched to form an ink chamber. Thus, a size of the ink chamber can be reduced. In addition, such a printhead is manufactured by an overall process without a bonding process. Thus, a process of manufacturing an ink-jet printhead having such a configuration is relatively simple.
In this configuration, however, the ink channel is placed in a straight line with the nozzle. Thus, when bubbles are generated, ink flows back toward the ink channel, thereby lowering an ejection property. In addition, the substrate exposed by the nozzle is etched to form the ink chamber. Accordingly, although the size of the ink chamber can be reduced, an ink chamber having a certain shape cannot be manufactured. Thus, it is difficult to manufacture an ink chamber having an optimum shape.
FIG. 3 schematically illustrates a cross-sectional view a structure of another conventional ink-jet printhead using a back-shooting method. Referring to FIG. 3, an ink-jet printhead includes a nozzle plate 50 in which a nozzle 51 is formed, an insulating layer 60 in which an ink chamber 61 and an ink channel 62 are formed, and a silicon substrate 70 on which a manifold 55 for supplying ink to the ink chamber 61 is formed. The nozzle plate 50, the insulating layer 60, and the silicon substrate 70 are sequentially stacked.
In such an ink-jet printhead, the ink chamber 61 is formed using the insulating layer 60 stacked on the substrate 70 such that the shape of the ink chamber 61 can be varied and the back flow of ink can be prevented.
In the manufacture of this ink-jet printhead, however, in general, a thick insulating layer is deposited on a silicon substrate and etched, thereby forming an ink chamber. Such a method has the following problems: first, it is difficult to stack a thick insulating layer on a substrate in a semiconductor manufacturing process, and second, it is difficult to etch a thick insulating layer. Thus, in this ink-jet printhead, there is a limitation on the depth of the ink chamber. An ink chamber and a nozzle having a depth of about 6 μm are shown in FIG. 3. It is virtually impossible, however, to manufacture an ink-jet printhead having a comparatively large drop size using an ink chamber having this depth.